This invention relates to a cylinder-number-controlled engine, and more specifically to a multicylinder engine whose working cylinders are variably controlled in number to suit operating requirements, with an air fuel mixture fed from a single throttle valve to the working cylinder or cylinders through an intake manifold, including at least one normally closed control valve installed in at least one intake pipe of the intake manifold, the control valve being adapted to open momentarily, independently of the throttle valve.
It is not uncommon these days that multicylinder engines are designed so that the number of working cylinders is increased or decreased according to the changing operating conditions of the engine. With a three-cylinder engine, for example, only one cylinder operates when the engine is idling or running under low-load condition. As the engine load increases, say at the vehicular velocity of about 40 kilometers an hour, one more cylinder joins. Under heavier loads all three cylinders take part in giving the necessary power output. In this manner the number of cylinders at work is controlled at all times to attain an optimum air fuel ratio and reduce fuel consumption. To realize this technical idea with multicylinder engines, usually one or more or all of the intake manifold pipe are equipped with a control valve each which is opened correspondingly to the opening of the throttle valve.
The existing arrangements, which thus invariably use control valves the opening of which corresponds to that of the throttle valve, have a common disadvantage in that, especially in the early stage of each control valve opening, the engine operates in an irregular combustion zone .alpha., as hatched in FIG. 1, gives a shock to the vehicle and mars riding comfort.